Cortical processing of sensory information plays a critical role in sensory discrimination, object recognition and memory. Cortical sensory processing has been shown to be highly dynamic, with past experience, current context and expectations shaping how the world is perceived on a moment by moment basis. Disorders of sensory processing constitute a major component of impairments induced by CNS disease and aging as well as congenital disorders such as autism. In the olfactory system, features of odorant molecules and mixtures are believed to be extracted by a large family of olfactory receptor proteins at the receptor sheet, and further defined by synaptic processing with the olfactory bulb. Current theories of olfactory function suggest that re-assembly of these features into perceptual odorant wholes is performed largely by circuits in the primary olfactory cortex. Work completed during the past funding period of this award provided evidence that receptive fields (RF's) of olfactory cortical neurons were highly dynamic, and appeared to be consistent with the synthetic role proposed for this cortex. Namely, single piriform cortex neurons showed a high degree of discrimination of molecularly similar odorants, whereas their primary afferent, mitral/tufted cells appeared to express feature detecting RF's. However, given the broad range of odorants and odorant mixtures that animals can discriminate, it is unlikely that cortical synthetic coding is due to innate hard-wiring, but rather reflects an experience-dependent, perceptual learning process that allows synthesis of novel co-occurring features. Using a multidisciplinary approach, the present proposal seeks further evidence of synthetic coding in the piriform cortex (Aim 1), and begins to explore the necessary conditions for, and mechanisms of, perceptual learning and formation of synthetic cortical RF's (Aims 2 & 3). [unreadable] [unreadable]